MLZ is a cooperation between:

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich
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MLZ (eng)

Lichtenbergstr.1
85748 Garching

MEPHISTO (under construction)

Facility for particle physics with cold neutrons

MEPHISTO scheme MEPHISTO scheme

Since the start of reactor the FRM II provides a cold white neutron beam for long term user dedicated experimental setups.

Such an experiment is normally planned and built up by external groups but additional help during the commissioning of the experiment at the reactor is necessary. Therefore, this work must be organised in close contact with the local instrument scientist. The desired precision is reached inter alia by good statistics which means long term experiments over several reactor cycles.

The experimental area MEPHISTO, the measurement facility for particle physics with cold neutrons, is dedicated to those experiments in the field of nuclear and particle physics. Currently, the experimental area moves from the Neutron Guide Hall West to the Neutron Guide Hall East. The solely used neutron guide SR-4b will deliver a white cold spectrum for experiments. A removeable 11% velocity selector at the end of the guide will complete the beam line.

The MC-simulation for this beam with a dimension of 60 x 106 mm² proposes a mean wavelength of 4.5 Å and a gold capture flux of 2·1010 n cm-1s-1. The experimental area is 5 × 25 m², diagonally built-in in the Neutron Guide Hall East. The spectrum shows a shoulder to smaller wavelengths, the maximum of the spectrum is located at 3.3 Å.

It is planned to install the instrument PERC [1] at the MEPHISTO beam line during the first years of operation in the Neutron Guide Hall East. This instrument is a precise, bright and intense source of protons and electrons from the neutron decay. The instrument PERC itself is open for external user groups with spectrometers to measure the protons and electrons.

[1] Dubbers, D. et al., Nucl.Instr.Meth. A, 596, 238-247, (2008)

Typical Applications

The experiments at MEPHISTO concentrate on induced nuclear reactions of the neutron with atoms or on the free neutron decay with its products.

Some of the experiment types performed at MEPHISTO:

  • Free neutron decay and spectroscopy of the decay products
  • Spectroscopy of neutron induced fission
  • Production of ultra cold neutrons with liquid helium
  • Production of ultra cold neutrons with solid gases
Infrastructure

A removeable neutron velocity selector is placed at the end of the neutron guide. The minimal wavelength is 4.5 Å. The resolution of the passing wavelength is 11%. The selector can be rotated to tune the resolution.

A data system based on VME (ADC, peak ADC, QDC, TDC) is available. For signal forming purpose several NIM inserts exist, a list can be requested from the local instrument scientist. Also available are spectroscopic amplifiers and high voltage sources for detectors.

Technical Data

Neutron beam

  • End of the cold neutron guide SR-4b (m = 2.5)
  • Cross section of the guide: 60 x 106 mm²
  • Thermal capture flux (simulated): 2·1010 n cm-1s-1
  • Mean wavelength (simulated): 4.5 Å
  • Beam height from floor: ~ 1300 mm
  • Experimental area: 5 × 25 m²
  • Maximum at 3.3 Å
  • Standard neutron spectrum with shoulder to smaller wavelengths

Beam attenuators

  • By geometrical attenuation, the beam intensity can by reduced to 20%, 4% and 2%

Polarisation

  • A bender (vertical direction) is available to polarise the complete cross section of the beam

Instrument Scientist

Dr. Jens Klenke
Phone: +49 (0)89 289-14771
E-Mail:

Operated by

TUM

Publications

Find the latest publications regarding MEPHISTO in our publication database iMPULSE:

impulse.mlz-garching.de

Instrument-DOI

doi:10.17815/jlsrf-1-48

Gallery

MEPHISTO
MEPHISTO
Neutron spectrum
Neutron spectrum

Figure 1: Simulated cold neutron spectrum of the SR4b at the MEPHISTO facility in neutron guide hall East.

Neutron velocity selector
Neutron velocity selector

Figure 2: Cutaway view of the removable neutron velocity selector at the end of the MEPHISTO guide.

MLZ is a cooperation between:

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Geesthacht> Helmholtz-Zentrum GeesthachtForschungszentrum Jülich> Forschungszentrum Jülich